TREATING SEPSIS

     
   

 

     
     

Step H - Hemodynamics: assess adequacy of resuscitation and prevention of organ failure.

Adequacy of resuscitation is evaluated by looking at endorgan perfusion – using clinical examination and interpretation of monitored variables. There is no ideal method (1).  There are a number of reliable, yet simple measures. Direct measurement of blood pressure (using an arterial line) is essential to guide therapy, and there is a strong relationship between restoration of blood pressure and urinary output. The central venous pressure is useful for monitoring volume status, but of little value in terms of organ perfusion. In the blood gas, the pH, base deficit and serum lactate are useful guides of all body perfusion and anaerobic metabolism. During the resuscitation process, the patient should become gradually less acidotic and the base deficit and serum lactate should reduce.

There are a number of more invasive measures of perfusion. Pulmonary artery catheters are inserted to construct pressure volume relationships of the left ventricle and to measure cardiac output. They are also useful devices for measuring oxygen consumption because they can equate mixed venous oxygen saturation to cardiac output. The normal mixed venous oxygen saturation is 70%. A very low mixed venous saturation (SVO2) is indicative of excessive extraction of oxygen per unit blood – “under-resuscitation”. A very high is difficult to interpret: it may represent the inability of the tissues to extract oxygen, which certainly occurs in sepsis, or it may just be due to hyperdynamic circulation and overall increased oxygen delivery. And this is the problem with SvO2: it is a very blunt measurement. A normal SvO2 may represent normal whole body oxygen utilization while small organs and tissue systems are literally rotting inside. Moreover, the pulmonary artery catheter is of uncertain benefit, particularly in sepsis (2).

The pulmonary artery catheter controversy has led to a variety of non invasive monitors of stroke volume: the esophageal doppler (3), the non invasive cardiac output monitor using CO2 rebreathing (NICO) (4) and lithium dilution (5). These techniques may represent great advances in monitoring volume resuscitation; however there is, to date, little evidence of efficacy (1) .

It is possible to measure mixed venous oxygen saturation from an adapted central venous catheter, which has been shown to be a good measure of adequacy of resuscitation (6).

There have been many recent attempts to localize measurement of tissue perfusion – by looking at regional circulation. The most widely adopted tools are jugular venous oxygen saturation (SjO2), which is used in head injury, and gastric tonometery, which is sometimes used in sepsis. The most recent variant of tonometery, regional capnometery, measures gastric carbon dioxide (CO2) production, by absorbing CO2 from an air filled balloon attached to a modified nasogastric tube, and end tidal CO2, from the ventilator circuit. The presence of a very high concentration of CO2 in the stomach or a wide gastric-end tidal CO2 gap, is believed to be indicative of poor splanchnic blood flow. There are, however, concerns about measurement error and interpretation, and this technique is not widely accepted (7).

In the end, monitors are fallible, and it is often useful to fall back on old fashioned instinct: how does the patient look? Do not rely on monitors and numbers to fully guide your management: look at the patient, be aware of the conventional clinical signs, as these are often the most reliable.

References

(1)   Dabrowski GP, Steinberg SM, Ferrara JJ, Flint LM. A critical assessment of endpoints of shock resuscitation. Surg Clin North Am 2000; 80(3):825-844.

(2)   Connors AF, Jr., Speroff T, Dawson NV, Thomas C, Harrell FE, Jr., Wagner D et al. The effectiveness of right heart catheterization in the initial care of critically ill patients. SUPPORT Investigators. JAMA 1996; 276(11):889-897.

(3)   Gan TJ, Bennett-Guerrero E, Phillips-Bute B, Wakeling H, Moskowitz DM, Olufolabi Y et al. Hextend, a physiologically balanced plasma expander for large volume use in major surgery: a randomized phase III clinical trial. Hextend Study Group. Anesth Analg 1999; 88(5):992-998.

(4)   de Abreu MG, Quintel M, Ragaller M, Albrecht DM. Partial carbon dioxide rebreathing: a reliable technique for noninvasive measurement of nonshunted pulmonary capillary blood flow. Crit Care Med 1997; 25(4):675-683.

(5)   Linton R, Band D, O'Brien T, Jonas M, Leach R. Lithium dilution cardiac output measurement: a comparison with thermodilution. Crit Care Med 1997; 25(11):1796-1800.

(6)   Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, Knoblich B et al. Early goal-directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med 2001; 345(19):1368-1377.

(7)   Creteur J, De Backer D, Vincent JL. Does gastric tonometry monitor splanchnic perfusion? Crit Care Med 1999; 27(11):2480-2484.

       
   

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